This invention relates to downhole tools used to collect samples in a wellbore. More particularly, but not by way of limitation, this invention relates to an apparatus and method of collecting multiple samples of fluid from an oil and gas reservoir that has been penetrated by a wellbore.
Various types of samplers have been used in the past. For instance, in U.S. Pat. No. 4,903,765 to Zunkel, there is disclosed a delayed opening fluid sampler containing multiple sample chambers. The sampler is lowered into the wellbore on a workstring to the desired depth. According to the techniques taught by Zunkel, in order to begin operation, a sufficient amount of annulus pressure must be applied to shear a set of holding pins. A fluid restriction was provided so that a time delay is established between the period from applying annulus pressure and the collecting of the sample.
Another type of fluid sampler is found in U.S. Pat. No. 4,665,983 to Ringgenberg. Again, this type of sampler is lowered into the wellbore to the desired depth, a port defined in the tool is opened in response to annulus pressure whereby the port admits well fluid into a sample chamber.
Also, applicant has submitted application Ser. No. 602,840, entitled "Wellbore Fluid Sampler" on Oct. 24, 1990, and application Ser. No. 602,823 on Oct. 24, 1990. These applications deal with samplers, and more particularly, to means of activating samplers. See also application Ser. No. 730,211 filed on Jul. 15, 1991 which pertains to a Shut-In Tool With Electric Timer.
The assignee of the present invention has also developed an annulus pressure responsive tool which operates in response to a relatively low annulus pressure increase as shown in U.S. Pat. Nos. 4,422,506 and 4,429,748, both to Beck and assigned to the assignee of the present invention.
These low pressure responsive tools shown in U.S. Pat. Nos. 4,422,506 and 4,429,748 have a power piston which is exposed to well annulus pressure from above, and which has its lower surface exposed to pressurized nitrogen gas in a nitrogen chamber located there below. Located below the nitrogen chamber is a metering chamber or equalizing chamber which is filled with oil. A floating piston separates the gas in the gas chamber from the oil in the metering chamber. Disposed in the metering chamber is a metering cartridge which provides a resistance to flow of oil therethrough. The lower end of the metering chamber below the metering cartridge is communicated with well annulus pressure, and a second floating piston separates the oil in the metering chamber from well fluid which enters the lower end of the metering chamber. An increase in well annulus pressure is immediately communicated to the upper surface of the power piston, but is delayed for a significant period of time in being fully communicated to the lower side of the power piston, so that a rapid increase in well annulus pressure will cause a downward pressure differential across the power piston to move the power piston and actuate the tool.
In U.S. Pat. No. 4,667,743 to Ringgenberg and Beck, the patent discloses an annulus, low pressure responsive flow tester valve having a lug and slot ratchet means operably connecting the ball valve of the tool with power piston.
In oil and gas operations, the operator often finds it desirable to retrieve multiple fluid samples taken at different time intervals. Moreover, the operator may wish to take multiple samples at different depth intervals in the wellbore. Prior art samplers simply have not been able to obtain multiple samples at different times and different intervals; therefore, there is a need in the industry for a sampler that can obtain multiple samples.